I'm looking for the most natural-sounding way to express the general concept of blue-green colours (such as cyan or teal) in Japanese. By "general concept", I mean all colours that are neither entirely blue nor entirely green, in shades ranging from dark to light. Here are some examples, taken from the CSS3 specification:

Aquamarine

Cyan

Turquoise

Teal

After a bit of research, I've come up with four possibilities.

青緑 / あおみどり / aomidori

This seems to be the best option (it literally translates as "blue-green") but I'm not sure whether or not it includes darker shades, such as teal.

2 Answers
2

The most generic would be 「[青緑色]{あおみどりいろ}」 or 「[青緑系]{あおみどりけい}の[色]{いろ}」-- especially the latter IMHO. It covers a wide range of tints and shades of greenish-blues.

「[水色]{みずいろ}」 is just light blue with absolutely no green in it. It is the name of one of the more common colors of crayon, so practically no native speakers would imagine a different color upon hearing the name.

「ターコイスブルー」 is as you said; It does not include a darker shade of green. Another problem is that not everyone would be familiar with the term.

「シアン」, I have never heard of. I am pretty sure most other native speakers would be unfamiliar with the word, too.

シアン is one of 色の四原色, and people who have bought a printer ink pack should be aware of that name. But it's rarely used in daily life, and AFAIK it always refers to that vivid #00FFFF -- 100% green plus 100% blue.
– narutoMay 5 '15 at 2:57

@naruto That agrees with the CSS3 definition linked to in the question - "cyan" is defined as #00ffff or 0,255,255.
– GoBustoMay 5 '15 at 7:55

I personally would just stick with plain 青い. Dictionaries will probably call it plain 'blue', and it does indeed lean more towards blue, but the point where people stop using it and start saying 緑 is pretty far into the green. The green light on traffic signals is typically called 青. Bananas can be called 青 before they turn ripe.

Japanese is a pretty broad language to begin with, and on top of that, color definitions will vary from person to person. This really is true for any language- for example, where's the border between red and pink? Each person will have a different answer based on their own experiences and mindset, so I wouldn't worry about getting it precise anyway. If you really need to emphasize that it's not exclusively blue, 青緑 would probably be okay, but if you're looking for the most natural-sounding option then 青い would definitely be the better choice, especially if you want to convey the "general concept".

I got this impression, but to give a bit more context: I'm working on a simple "What Is This Noun In Language X?" Javascript program (online version / source code) as a self-testing tool/coding exercise. I now want to add a "colours" category, with 12 basic colours: Red, Orange, Yellow, Green, Turquoise, Blue, Purple, Pink, Brown, Black, Grey, and White. I'm currently leaning towards 青緑 for "turquoise", though I'm half-tempted to simply remove it altogether to entirely avoid any ambiguity.
– GoBustoMay 5 '15 at 8:17